JP5510151B2 - Abrasive cloth and method for producing the same - Google Patents

Description

  The present invention relates to a polishing cloth, and particularly to a polishing cloth that can be suitably used when an aluminum alloy substrate or a glass substrate used for a magnetic recording disk is subjected to polishing and / or cleaning processing with an ultra-high precision finish. .

With the recent increase in storage density, magnetic recording disks are required to be smooth to the limit of the disk surface. In recent recording methods, since perpendicular recording media in which the easy axis of magnetization in the magnetic film is oriented in the vertical direction have become mainstream, if there are irregularities or scratches on the substrate before the magnetic layer is formed, the magnetic film is magnetized after film formation. There is a risk that the easy axis may become an abnormal portion of tilt. Therefore, it is required that the surface of the disk before forming the magnetic film has a substrate surface roughness of 0.1 nm or less and minimizes scratches on the substrate surface called scratch defects. Also, in the recording method after the perpendicular recording medium, the requirement for the substrate before the magnetic layer is formed is smoothing to the limit as described above.
Slurry grinding is performed on the magnetic recording disk substrate with a polishing pad made of hard polyurethane foam, etc., and then free abrasive grains are adhered to the surface of the polishing cloth in order to increase the smoothness by grinding minute scratches and protrusions. A method of performing polishing is used.

  Specifically, the polishing process is performed by continuously reciprocating the substrate in the radial direction of the substrate while pressing the tape-like polishing cloth (polishing tape) against the substrate with a rubber roller while the substrate of the magnetic recording disk is continuously rotated. The abrasive tape is run. At this time, the slurry is supplied between the polishing tape and the substrate, and the free abrasive grains contained in the slurry are gripped in a state of being finely dispersed in the fibers on the surface of the polishing tape and pressed against the substrate for polishing. It is. In the same process, a cleaning process that does not use loose abrasive grains is also performed.

  As polishing cloths used in polishing and cleaning processes, conventionally, the fibers constituting the nonwoven fabric are made ultrafine to reduce the substrate surface roughness of the magnetic recording disk, and the nonwoven fabric is impregnated with an elastic polymer to provide cushioning properties. It has been proposed that the scratch defects are minimized by making them, and certain results have been achieved (see Patent Documents 1 to 4).

However, in the above-mentioned conventional polishing cloth, the dispersion state of the ultrafine fibers on the surface cannot be said to be a sufficient level, and the twist of the ultrafine fibers is likely to occur during the polishing process, and the twisted bundle of ultrafine fibers strongly grips the abrasive grains. By doing so, the substrate surface tends to be deeply scratched, and the scratch performance tends to be lowered.
In addition, as a napping method of the polishing cloth, a method of adjusting the buff stage number, sandpaper count, grinding weight in each stage, sandpaper traveling speed, and sheet traveling speed has been proposed, and the napped fibers of the polishing cloth are densified, It has succeeded in reducing the direction of napping (see Patent Document 5). However, this proposal only describes general buffing conditions that are common to all artificial leather. For example, when the fiber diameter of ultrafine fibers is made thin, it is difficult to achieve optimum conditions. there were. That is, even when the fiber diameter of the polishing cloth is changed, it is required to set a universal napping condition for obtaining a surface capable of maintaining sufficient dispersibility.

Japanese Patent Laid-Open No. 2001-1252 JP 2002-273650 A Japanese Patent No. 3457478 JP 2007-144614 A Japanese Patent No. 4423915

  SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing cloth that can suppress scratch defects as compared with conventional polishing cloths while achieving reduction in substrate surface roughness.

  That is, the present invention is intended to solve the above-mentioned problem, and is composed of a fiber entangled body mainly composed of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm and an elastic polymer, and the surface ultrafine fibers are raised. The tip of the ultrafine fiber of 50.0 to 100.0% of the raised ultrafine fiber has a diameter of 120 to 300% of the fiber diameter. A polishing cloth.

Moreover, the manufacturing method of the polishing cloth of the present invention allows a sheet composed of a fiber entangled body mainly composed of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm and an elastic polymer to travel, and A sandpaper having an average abrasive grain size 10 to 90 times the average fiber diameter is rotated in the opposite direction to the traveling direction of the sheet running at a speed 100 to 160 times the sheet speed, so that the total grinding amount is 10 It is a manufacturing method of polishing cloth characterized by carrying out buffing grinding in a range of ˜80 g / m ² and a grinding load in the range of 200 to 1000 W / m.

  According to the preferable aspect of the manufacturing method of the abrasive cloth of this invention, the contact length of a sheet | seat and sandpaper is the range of 5-50 mm at the time of the said buffing grinding.

  According to the preferable aspect of the manufacturing method of the polishing cloth of the present invention, the grinding clearance is in the range of 0.1 to 0.9 times the target thickness during the buffing grinding.

  According to the present invention, by improving the dispersion state of the surface fibers of the polishing cloth, it is possible to make it less likely to cause defects such as scratches due to fiber twisting and fusion as compared with conventional polishing cloths. And the substrate surface can be smoothed.

FIG. 1 is a drawing-substitute SEM enlarged (2000 ×) photograph showing an example of the surface of the polishing cloth of the present invention. FIG. 2 is a SEM enlarged (40 ×) photograph of the polishing cloth surface obtained in Example 2 of the present invention.

  The abrasive cloth of the present invention is an abrasive cloth composed of a fiber entanglement mainly composed of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm and an elastic polymer, and the surface ultrafine fibers are raised. It has a fiber entanglement such as a nonwoven fabric formed by entanglement of a bundle (extra fine fiber bundle). In the present invention, by using ultrafine fibers, the surface roughness of the object to be polished can be reduced, and defects such as scratches can be made difficult to occur.

  Examples of the polymer that forms the ultrafine fiber include polyester, polyamide, polyolefin, polyphenylene sulfide (PPS), and the like. Many polycondensation polymers represented by polyester and polyamide have a high melting point, and are excellent in heat resistance against heat generated during polishing and are preferably used. Specific examples of the polyester include polyethylene terephthalate, polybutylene terephthalate, and potytrimethylene terephthalate. Specific examples of the polyamide include nylon 6, nylon 66, nylon 12, and the like.

  In addition, the polymer constituting the ultrafine fiber may be copolymerized with other components, or may contain additives such as particles, flame retardant, and antistatic agent.

  It is important that the average fiber diameter of the ultrafine fibers is 0.1 to 3.0 μm. By setting the average fiber diameter to 3.0 μm or less, preferably 2.5 μm or less, the surface roughness of the object to be polished can be reduced. On the other hand, when the average fiber diameter is 0.1 μm or more, preferably 0.3 μm or more, the fiber strength and rigidity can be maintained, so that polishing can be performed efficiently.

  As a form of the ultrafine fiber bundle, the ultrafine fibers may be slightly separated from each other, may be partially bonded, or may be aggregated. Here, the bond refers to a chemical reaction or physical fusion, and the aggregation refers to a molecular force such as a hydrogen bond.

  In a fiber entangled body such as a nonwoven fabric used for the polishing cloth of the present invention, fibers thicker than the ultrafine fibers defined above may be mixed. By mixing thick fibers, the strength of the polishing cloth can be reinforced and characteristics such as cushioning can be improved. As a polymer which forms a fiber thicker than such an ultrafine fiber, the same polymer as that constituting the aforementioned ultrafine fiber can be employed. The blending amount of the fibers thicker than the ultrafine fibers with respect to the nonwoven fabric is preferably 30% by mass or less, more preferably 10% by mass or less, so that the smoothness of the polishing cloth surface can be maintained. Moreover, it is preferable that the said thick fiber is not exposed to the surface from a viewpoint of polishing performance.

  As will be described later in the measurement methods of the examples, in the present invention, when fibers having a fiber diameter exceeding 10 μm are mixed, the fibers are not considered as ultrafine fibers and are measured from the average fiber diameter. Shall be excluded.

  As the nonwoven fabric which is a fiber entangled body used in the polishing cloth of the present invention, a short fiber nonwoven fabric obtained by forming a laminated fiber web using short fibers with a card and a cross wrapper and then performing needle punching or water jet punching Alternatively, a long-fiber nonwoven fabric obtained from a spunbond method or a melt blow method, a nonwoven fabric obtained from a papermaking method, or the like can be appropriately employed. Especially, the short fiber nonwoven fabric and the spun bond nonwoven fabric can obtain the aspect of the ultrafine fiber bundle as described later by needle punching.

  In the polishing cloth of the present invention, the fiber entangled body needs to contain an elastic polymer. By containing the elastic polymer, it is possible to prevent the ultrafine fibers from falling off from the polishing cloth due to the binder effect of the elastic polymer, and to form uniform napping at the time of raising. Moreover, by containing an elastic polymer, cushioning properties can be imparted to the polishing cloth and scratch defects can be reduced.

  Examples of the elastic polymer used in the present invention include polyurethane, polyurea, polyurethane / polyurea elastomer, polyacrylic acid, acrylonitrile / butadiene elastomer, and styrene / butadiene elastomer. Among these, polyurethane elastomers such as polyurethane and polyurethane / polyurea elastomer are preferably used.

  As the polyol component of the polyurethane-based elastomer, polyester-based, polyether-based and polycarbonate-based diols, or copolymers thereof can be used. Moreover, aromatic diisocyanate, alicyclic isocyanate, aliphatic isocyanate, etc. can be used as a diisocyanate component.

  The weight average molecular weight of the polyurethane elastomer is preferably 50,000 to 300,000. By setting the weight average molecular weight to 50,000 or more, more preferably 100,000 or more, and further preferably 150,000 or more, it is possible to maintain the strength of the polishing cloth and prevent the fine fibers from falling off. Further, by setting the weight average molecular weight to 300,000 or less, more preferably 250,000 or less, it is possible to suppress the increase in the viscosity of the polyurethane solution and facilitate the impregnation of the ultrafine fiber layer.

  The elastic polymer may contain polyester resins, polyamide resins, polyolefin resins, etc., acrylic resins, ethylene-vinyl acetate resins, and the like. Moreover, it is preferable to contain the content rate of these resin in the range which does not impair the characteristic of a polyurethane. As a content rate, the range of 0-30 mass% is preferable, More preferably, it is the range of 0-20 mass%.

  In addition, additives such as colorants, antioxidants, antistatic agents, dispersants, softeners, coagulation modifiers, flame retardants, antibacterial agents, and deodorizers are blended in the elastic polymer as necessary. Also good.

  The content of the elastic polymer is preferably 5 to 200% by mass with respect to the fiber structure formed by entanglement of the ultrafine fiber bundle. Depending on the content of the elastic polymer, the surface state, cushioning properties, hardness, strength, and the like of the polishing cloth can be adjusted. By setting the content of the elastic polymer to 5% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, fiber dropping can be reduced. On the other hand, when the content of the elastic polymer is 200% by mass or less, more preferably 100% by mass or less, and further preferably 80% by mass or less, processability and productivity are improved, and ultrafine fibers are formed on the surface. A uniformly dispersed state can be obtained.

The basis weight of the portion of the polishing cloth of the present invention excluding the reinforcing layer described later is preferably 100 to 600 g / m ² . By setting the basis weight to 100 g / m ² or more, more preferably 150 g / m ² or more, it is excellent in the form stability and dimensional stability of the polishing cloth. Can be suppressed. On the other hand, when the basis weight is 600 g / m ² or less, more preferably 300 g / m ² or less, the handling property of the polishing tape becomes easy, and the cushioning property of the polishing cloth is moderately suppressed. The pressing pressure by the rubber roller from the surface can be appropriately propagated to the polishing surface, and efficient polishing can be performed.

  Moreover, the thickness of the part except the reinforcement layer mentioned later of the polishing cloth of this invention becomes like this. Preferably it is 0.1-10 mm. By setting the thickness to 0.1 mm or more, preferably 0.3 mm or more, the shape and dimensional stability of the polishing cloth are excellent, and processing unevenness and scratch defects due to elongation of the polishing cloth during polishing processing are suppressed. be able to. On the other hand, by setting the thickness to 10 mm or less, more preferably 5 mm or less, the pressing pressure at the time of polishing can be sufficiently propagated.

  Moreover, it is also a preferable aspect that the polishing cloth of the present invention has a reinforcing layer on the other surface of the ultrafine fiber raised surface (surface to be subjected to polishing) described later. By providing the reinforcing layer, the polishing cloth is excellent in form stability and dimensional stability, and processing unevenness due to elongation of the polishing cloth during polishing and generation of scratch defects can be suppressed.

  As the reinforcing layer, a woven fabric, a knitted fabric, a nonwoven fabric (including paper), a film-like material (plastic film, metal thin film sheet, etc.), and the like can be employed.

  In the polishing cloth of the present invention, it is important that the tip portion of 50.0 to 100.0% of the ultrafine fibers raised has a diameter of 120 to 300% of the fiber diameter. As described above, the state in which the tip of the ultrafine fiber has a diameter of 120 to 300% of the fiber diameter is a state in which a protrusion such as a spherical shape is formed at the tip of the ultrafine fiber. Say. Since the tip of the ultrafine fiber has a diameter of 120 to 300% of the fiber diameter, it is possible to maintain an appropriate distance between the ultrafine fibers and to obtain the dispersibility of the raised ultrafine fibers. In addition, since the tip portion is not too large in diameter, it does not induce defects such as scratches on the surface of the substrate due to the projections such as a spherical shape at the tip portion. The diameter of the tip is preferably in the range of 130 to 280%, more preferably in the range of 140 to 260% with respect to the fiber diameter.

  Also, as shown in FIG. 1, the protrusions at the tip are mostly spherical (spherical tip 1), but are polygonal (polygonal tip 2) represented by a trapezoidal shape. Is also a protrusion. Moreover, about a polygonal processus | protrusion, the part which has the largest diameter (width | variety) shall be measured as a magnitude | size of a processus | protrusion.

  Further, the tip of the ultrafine fiber refers to a portion existing within 50 μm from the tip of the ultrafine fiber. Protrusions existing on the inner side (abrasive cloth side) beyond 50 μm from the tip of the ultrafine fiber are not counted as protrusions at the tip as nodes or foreign matters.

  Moreover, in this invention, it is important that the raising | fluff which has a protrusion in the front-end | tip part of the said ultrafine fiber exists in the range of 50.0-100.0% of all the measured ultrafine fibers. Sufficient dispersibility can be obtained by providing 50.0% or more of raised hairs having protrusions, and dispersibility can be further improved by setting the amount to 60.0% or more.

  In the polishing cloth of the present invention, it is important that the surface on the side subjected to polishing is subjected to raising treatment and has napping. By forming the napping, the dispersion of the ultrafine fibers as described above can be obtained, and further, the cushioning property suitable for the surface fibers can be obtained, so that the scratch defects can be further reduced.

  The napped length of the polishing cloth of the present invention is preferably in the range of 0.1 to 2.0 mm. When the napped length is longer than 2.0 mm, twisting between ultrafine fibers is likely to occur during polishing, and the scratch performance is lowered. In addition, when the napped length is less than 0.1 mm, the area of the raised ultrafine fibers existing on the surface of the polishing cloth is reduced, so that the abrasive grains are likely to aggregate in a portion where the napped is not present, resulting in processing unevenness and scratch performance. Incurs a decline.

  As will be described in detail later, in order to obtain the ultrafine fiber tip as described above, the sandpaper speed suitable for the abrasive fiber sheet processing speed suitable for the ultrafine fiber size during the raising treatment By taking appropriate grinding amount, grinding load, sheet-sandpaper contact length and grinding clearance, the ultrafine fibers combined with polyurethane are efficiently dug up, and the ultrafine fibers are slightly stretched by the sandpaper abrasive grains After being torn off, the stretched portion contracts, and a protrusion such as a spherical shape having a diameter larger than that of the ultrafine fiber is formed at the tip.

  Next, a method for producing the polishing cloth of the present invention will be described.

  As a means for obtaining a fiber entanglement such as a nonwoven fabric formed by entanglement of ultrafine fiber bundles, it is preferable to use ultrafine fiber generating fibers. Although it is difficult to produce a fiber entanglement directly from an ultrafine fiber, a fiber entanglement is produced from an ultrafine fiber-generating fiber, and an ultrafine fiber is generated from a sea-island composite fiber in the fiber entanglement. A fiber entangled body in which the bundle is entangled can be obtained.

  As ultra-fine fiber-generating fibers, two-component thermoplastic resins with different solvent solubility are used as sea components and island components, and the sea components are dissolved and removed using a solvent, etc., so that the island components are made into ultra-fine fibers. Alternatively, a two-component thermoplastic resin may be alternately disposed in a radial or multilayer manner on the fiber cross section, and a peelable composite fiber that is split into ultrafine fibers by separating and separating each component may be employed.

  For sea-island type fibers, sea-island type composite fibers that use a sea-island type composite base to spun two components of the sea component and the island component, and mixed spinning that mixes and spins the two components of the sea component and the island component are spun. Although there are fibers and the like, sea-island type composite fibers are preferably used from the viewpoint that ultrafine fibers having a uniform fineness are obtained, and that a sufficiently long ultrafine fiber is obtained and contributes to the strength of the sheet-like material.

As the sea component of the sea-island fiber, polyethylene, polypropylene, polystyrene, copolymer polyester obtained by copolymerizing sodium sulfoisophthalic acid, polyethylene glycol, or the like, and polylactic acid can be used.
The dissolution removal of the sea component may be performed at any timing before, after applying, and after raising the elastic polymer.
As a method for obtaining a fiber entangled body such as a nonwoven fabric, as described above, a method of entanglement of a fiber web with a needle punch or a water jet punch, a spun bond method, a melt blow method, a paper making method, etc. can be adopted. In order to achieve the above-described form of the ultrafine fiber bundle, it is preferable to undergo treatment such as needle punching or water jet punching.

  In the needle used for the needle punching process, the number of needle barbs (cuts) is preferably 1 to 9. By using one or more needle barbs, efficient fiber entanglement becomes possible. On the other hand, fiber damage can be suppressed by using 9 or less needle barbs.

  The total depth of the needle barb is preferably 0.04 to 0.09 mm. By setting the total depth to 0.04 mm or more, a sufficient catch on the fiber bundle can be obtained, so that efficient fiber entanglement is possible. On the other hand, fiber damage can be suppressed by setting the total depth to 0.09 mm or less.

The number of punching is preferably 1000 to 4000 / cm ² . By setting the number of punching to 1000 pieces / cm ² or more, denseness can be obtained and high-precision finishing can be obtained. On the other hand, when the number of punching is 4000 / cm ² or less, deterioration of workability, fiber damage, and strength reduction can be prevented.

  Moreover, when performing a water jet punch process, it is preferable to perform water in the state of a columnar flow. Specifically, water may be ejected from a nozzle having a diameter of 0.05 to 1.0 mm at a pressure of 1 to 60 MPa.

The apparent density of the ultrafine fiber generating fiber nonwoven fabric (fiber entangled body) after the needle punching process or water jet punching process is preferably 0.15 to 0.35 g / cm ³ . By setting the apparent density to 0.15 g / cm ³ or more, the polishing cloth has excellent shape stability and dimensional stability, and can suppress the processing unevenness due to the elongation of the polishing cloth and the occurrence of scratch defects. . On the other hand, by setting the apparent density to 0.35 g / cm ³ or less, a sufficient space for applying the elastic polymer can be maintained.

  From the viewpoint of densification, the ultrafine fiber-generating fiber nonwoven fabric (fiber entangled body) thus obtained is preferably shrunk by dry heat or wet heat, or both, and further densified. Moreover, you may compress in the thickness direction by a calendar process etc.

  As the solvent for dissolving the easily soluble polymer (sea component) from the ultrafine fiber generating fiber, if the sea component is a polyolefin such as polyethylene or polystyrene, an organic solvent such as toluene or trichloroethylene is used. In the case of a copolyester, an alkaline aqueous solution such as sodium hydroxide can be used. Further, the ultrafine fiber generation processing (sea removal treatment) can be performed by immersing the ultrafine fiber generation type fiber (nonwoven fabric made of) in a solvent and squeezing it.

  In addition, for the ultrafine fiber generation processing, known apparatuses such as a continuous dyeing machine, a vibro-washer type sea removal machine, a liquid dyeing machine, a Wins dyeing machine, and a jigger dyeing machine can be used. The ultrafine fiber generation processing may be performed before the napping treatment or after the napping treatment.

  In addition, in order to obtain the fineness and uniformity of the fiber distribution on the surface of the polishing cloth, the elastic polymer mainly composed of polyurethane is a nonwoven fabric (fiber entangled body) in which fiber bundles of ultrafine fibers are entangled. It is preferable that the microfiber is not substantially present inside the fiber bundle. When the elastic polymer is present even inside the fiber bundle, the elastic polymer is present by adhering to each ultrafine fiber, so that the surface fibers are easily torn during the buffing process and it is difficult to form napped hairs.

As a method of obtaining a form in which the elastic polymer does not substantially exist inside the fiber bundle of ultrafine fibers, the elastic polymer is made into a solution with a solvent such as dimethylformamide,
(1) After impregnating the elastic polymer solution into a nonwoven fabric (fiber entangled body) entangled with an ultra-fine fiber generating type sea-island type composite fiber, and coagulating it in water or an organic solvent aqueous solution, A method of dissolving and removing the sea component with a solvent that does not dissolve the elastic polymer,
(2) After applying a polyvinyl alcohol having a saponification degree of preferably 80% or more to a nonwoven fabric entangled with an ultra-fine fiber generating type sea-island composite fiber, and protecting most of the periphery of the fiber, A method in which the sea component is dissolved and removed with a solvent that does not dissolve polyvinyl alcohol, then impregnated with an elastic polymer solution, solidified in water or an organic solvent aqueous solution, and then the polyvinyl alcohol is removed can be preferably used. .

  As a solvent used when the elastic polymer is applied to the fiber entanglement, N, N′-dimethylformamide, dimethyl sulfoxide, or the like can be preferably used. Alternatively, an aqueous polyurethane dispersed as an emulsion in water may be used.

  The elastic polymer is applied to the fiber entangled body by immersing the fiber entangled body in an elastic polymer solution dissolved in a solvent, and then dried to substantially solidify and solidify the elastic polymer. In drying, the fiber entangled body and the elastic polymer may be heated at a temperature that does not impair the performance.

  Thus, the raising | fluff process of the sheet | seat for polishing cloths obtained can be performed using a sandpaper, a roll sander, etc. In particular, by using sandpaper, uniform and dense napping can be formed. Furthermore, in order to form the above-mentioned uniform ultrafine fiber napping on the surface of the polishing cloth, (1) the ratio of the abrasive grain size of the sandpaper used with the ultrafine fiber, (2) the sandpaper and the sheet speed It is necessary to control the ratio, (3) grinding amount, and (4) grinding load within an appropriate range. In order to reduce the grinding load, multi-stage buffing with 3 or more buff stages is used, with 70 to 90% of the total grinding amount in the first and second stages or more, and 30 to 10% in the final stage. It is preferable to carry out and prepare the surface. In the case of three-stage buffing, it is preferable to set the total grinding amount to 50 to 70% at the first stage, 20 to 30% at the second stage, and 10 to 20% at the third stage. It is preferable that coarse thickness adjustment is performed by grinding 50% or more in the first stage, and finishing is performed in the second and third stages. Specifically, it is preferable to perform finish grinding by grinding the half of the first stage in the second stage and grinding the half of the second stage in the second stage.

  In order to perform the above-mentioned raising treatment, it is important to (1) surface grind using an abrasive sandpaper having an average particle diameter of 10 to 90 times the average fiber diameter of the ultrafine fibers. By setting the average abrasive particle size to the above range with respect to the average fiber diameter, it is possible to efficiently raise the ultrafine fibers combined with the elastic polymer to form napped, It is possible to make it difficult to cause fusion or the like. The average abrasive particle size with respect to the fiber diameter is preferably 15 to 85 times, more preferably 20 to 80 times.

  (2) Regarding the relationship between the speed of the sandpaper and the sheet speed, it is important to rotate the sandpaper at a speed of 100 to 160 times the traveling direction of the sheet in the direction opposite to the traveling direction of the sheet. By setting the sheet speed and the sandpaper speed within the above ranges, it is possible to suppress the grinding load and make it difficult to cause fusion between ultrafine fibers.

  The speed of the sandpaper is preferably 400 to 1500 m / min, more preferably 500 to 1200 m / min. The sheet speed is preferably 3.0 to 18.0 m / min, and more preferably 4.0 to 16.0 m / min. The sandpaper speed is preferably 100 to 160 times, more preferably 105 to 155 times the sheet speed.

In addition, it is important that the amount of grinding by (3) buffing grinding is 10 to 80 g / m ² . By setting the grinding amount to 10 g / m ² or more, sufficient quality can be obtained, and by setting the grinding amount to 80 g / m ² or less, fiber fusion can be suppressed. The grinding amount is preferably 20 to 70 g / m ² , more preferably 30 to 60 g / m ² .

  Further, it is important that the grinding load in (4) buffing grinding is in the range of 200 to 1000 W / m, and the grinding load is preferably in the range of 300 to 900 W / m. By setting the grinding load to 1000 W / m or less, it becomes possible to effectively cut out ultrafine fibers without causing fiber fusion or the like. By setting the grinding load to 200 W / m or more, sufficient grinding can be achieved. Can be implemented. In the case of multistage buffing, the maximum load in each stage needs to be within the above range.

  Further, the contact length between the sheet and the sandpaper in the buffing grinding is preferably in the range of 5 to 50 mm, more preferably in the range of 10 to 40 mm with respect to the full width in the sheet traveling direction. By making the contact length 5 mm or more, it is possible to maintain a grinding length sufficient for buffing, and by making the contact length 50 mm or less, the load on the sheet can be reduced to a certain level or less. No fusing or the like occurs.

  In addition, the grinding clearance in the buffing grinding is preferably 0.1 to 0.9 times, more preferably 0.2 to 0.8 times the target thickness. By setting the grinding clearance to 0.1 times or more, it is possible to maintain a pressing state that does not break the sheet, and by setting the grinding clearance to 0.9 times or less, it is possible to maintain a sufficient pressing state of the sandpaper. .

  By buffing and grinding under the above conditions, ultrafine fibers bonded to an elastic polymer such as polyurethane were efficiently dug up, and each of the dugout ultrafine fibers was slightly stretched by sandpaper abrasive grains. By being torn off later, the stretched portion contracts, and a spherical or polygonal protrusion having a diameter larger than that of the ultrafine fiber is formed at the tip.

  In the photograph of FIG. 4 of Patent Document 5, the tip of the polishing cloth surface fiber appears to be partially spherical, but the grinding ratio and grinding load of the three-stage buffing are different from the polishing conditions of the present invention. For this reason, there are only about 20 to 40% of ultrafine fibers having a tip having a diameter of 120 to 300% of the fiber diameter.

  The polishing cloth of the present invention can be used, for example, as a polishing tape or a cleaning tape by cutting into a tape having a width of 30 to 50 mm from the viewpoint of processing efficiency and stability.

  As a polishing method, a magnetic recording disk substrate made of an aluminum alloy or the like can be polished using the polishing tape as described above and a slurry containing loose abrasive grains. As the slurry, those obtained by dispersing high-hardness abrasive grains such as diamond fine particles in an aqueous dispersion medium are preferably used. The abrasive grain size is preferably 100 nm or less from the viewpoint of retention and dispersibility of abrasive grains suitable for the ultrafine fibers constituting the polishing cloth of the present invention.

  In addition, the polishing cloth of the present invention can be preferably used for cleaning processing that does not use loose abrasive grains.

[Measuring method and processing method for evaluation]
(1) Melting Point Using a DSC-7 manufactured by Perkin Elmer, the peak top temperature indicating the melting of the polymer at 2nd run was defined as the melting point of the polymer. At this time, the rate of temperature increase was 16 ° C./min, and the sample amount was 10 mg.

(2) Melt flow rate (MFR)
4-5 g of sample pellets are placed in a cylinder of an MFR electric furnace and the amount of resin extruded in 10 minutes under a load of 2160 gf and a temperature of 285 ° C. using a Toyo Seiki melt indexer (S101) (g) Was measured. The same measurement was repeated 3 times, and the average value was defined as MFR.
(3) Grinding load at the time of buffing processing In the buffing process at the time of raising the surface of the polishing cloth, the power applied to the rotation of the sandpaper when not in contact with the sheet: the work amount (W0) is measured in advance, and then the sheet is The electric power (W1) when the through buffing process was performed was measured, and the electric power (W2) required for the buffing process was calculated from W1-W0. In the case of multi-stage buffing, if even one stage with a high grinding load is affected by fusion, the value of the stage with the largest grinding load is taken as the maximum grinding load.

(4) Average fiber diameter of ultrafine fibers A cross section perpendicular to the thickness direction including the ultrafine fibers of the polishing cloth was observed at a magnification of 3000 using a scanning electron microscope (VE-7800 manufactured by SEM KEYENCE), and was 30 μm × 30 μm. The diameters of 50 single fibers extracted at random within the visual field were measured in μm units with 3 significant digits. However, this was performed at three locations, the diameter of a total of 150 single fibers was measured, and the third significant digit was rounded off to calculate the average value with two significant digits. When fibers having a fiber diameter exceeding 10 μm are mixed, the fibers are excluded from the measurement target of the average fiber diameter as not corresponding to the ultrafine fibers. When the ultrafine fiber has an irregular cross section, first, the cross sectional area of the single fiber is measured, and the diameter of the single fiber is calculated by calculating the diameter when the cross section is regarded as a circle.

(5) Fiber diameter of the tip of the ultrafine fiber on the surface of the polishing cloth The surface of the polishing cloth was photographed at a magnification of 2000 using an SEM, and three ultrafine fibers present in the obtained photograph with which the tip portion can be clearly confirmed Extraction was performed, the diameter in the direction perpendicular to the fiber diameter of the tip portion was measured, and the value divided by the fiber diameter of the ultrafine fiber was calculated as a percentage. This was performed at 10 locations, and the average value of 30 ultrafine fibers was calculated.

(6) Polishing process A polishing cloth was used as a tape having a width of 30 mm. As a polishing target, a glass substrate made of amorphous glass manufactured by KMG whose surface roughness was controlled to 0.3 nm or less was used. A slurry having a concentration of 0.01% of free abrasive grains in which single crystal diamond particles having a primary particle diameter of 5 nm were clustered to an average diameter of 80 nm was dropped onto the polishing cloth surface at a rate of 50 ml / min. Further, the tape running speed was 70 mm / min, the disk rotation speed was 600 rpm, the swing was 100 times / min, the pressing pressure was 1.5 kgf, and polishing was performed for 15 seconds. This was performed on both sides of each disk.

(7) Substrate Surface Roughness Measured in a tapping mode using “AFM NanoScope” (registered trademark) IIIa manufactured by Veeco. The observation area on the substrate was 10 μm × 10 μm, an arbitrary point on the substrate was measured, and the average value of the arbitrary three points was defined as the surface roughness (Ra).

(8) Scratch point Using both the surface of 5 substrates after polishing, that is, the total area of the surface of 10 substrates as a measurement object, using an optical surface analyzer (Candela 6100), the scratch point is determined by scratching a groove having a depth of 5 nm or more. It measured and evaluated by the average value of the measured value of 10 surfaces. The lower the value, the higher the performance.

[Example 1]
(raw cotton)
(Sea component and island component)
Nylon 6 having a melting point of 220 ° C. and MFR 58.3 was used as an island component, and copolymerized polystyrene (co-PSt) obtained by copolymerizing 22 mol% of 2-ethylhexyl acrylate having a melting point of 53 ° C. and MFR 300 was used as a sea component.

(Spinning / drawing)
Using the above-mentioned island component and sea component, using a 376 island / hole sea-island type composite die, spinning temperature 285 ° C., island / sea mass ratio 40/60, discharge rate 1.9 g / min / hole, spinning speed 1000 m Melt spun at / min. Next, the film is stretched 3.0 times in a liquid bath at a temperature of 85 ° C., crimped using an indentation type crimper, cut, and the single fiber fineness is 4.7 dtex and the fiber length is 51 mm. The raw cotton of sea-island type composite fiber was obtained.

(Extra-fine fiber generation type nonwoven fabric)
A laminated fiber web was formed through the carding process and the cross wrapping process using the raw cotton of the above-mentioned sea-island type composite fibers. Next, the obtained laminated fiber web was needle punched at a needle depth of 8 mm and a number of punches of 2000 / cm ² using a needle punch machine in which one needle having a total barb depth of 0.08 mm was implanted, and the basis weight was 700 g. An ultrafine fiber-generating fiber nonwoven fabric having an / m ² apparent density of 0.219 g / cm ³ was produced.

(Polishing cloth)
The ultrafine fiber generating fiber nonwoven fabric was subjected to hot water shrinkage treatment at a temperature of 95 ° C., and then 24 wt% polyvinyl alcohol was added to the fiber mass, followed by drying. The nonwoven fabric obtained in this way was provided with 21% by mass of a solid content with respect to the fiber mass of polyurethane consisting of 75% by mass of a polyether diol and 25% by mass of a polyester, and a liquid temperature of 35 ° C. The polyurethane was coagulated with 30% DMF aqueous solution and treated with hot water at a temperature of about 85 ° C. to remove DMF and polyvinyl alcohol. Thereafter, the sheet was cut in the thickness direction by a half-cutting machine having an endless band knife. Using the sandpaper having an average abrasive particle size of 55 μm (ratio of abrasive particle size / ultrafine fiber diameter: 75), the speed of the sandpaper is 800 m / min, and the non-semi-finished surface of the obtained sheet is in the opposite direction to the rotation of the sandpaper. The sheet speed is 5.3 m / min (ratio: 151), the contact length of the sandpaper is 40 mm, the clearance is 0.7 times the target thickness, and the grinding amount is 60:30:10 by three-stage buffing. In this ratio, a polishing cloth having napped bristles produced by buffing grinding was prepared with a total grinding amount of 50 g / m ² , a maximum grinding load of 600 W / m.

The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 0.73 μm, a thickness of 0.53 mm, a basis weight of 175 g / m ² , and an apparent density of 0.330 g / cm ³ . When the polishing performance was evaluated using the obtained polishing cloth, the substrate surface roughness and the number of scratches were satisfactory, and the surface after polishing was also highly uniform. The results are shown in Table 1.

[Example 2]
(raw cotton)
A single fiber fineness of 5.6 dtex and a fiber length of 51 mm were used in the same manner as in Example 1 except that a sea-island type composite base with 200 islands / hole was used and the discharge rate was 2.0 g / min / hole. A raw cotton of sea-island type composite fiber was obtained.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using a sandpaper with an average abrasive particle size of 90 μm (ratio of abrasive particle size / ultrafine fiber diameter: 82), a paper speed of 1000 m / min, a sheet speed of 10.0 m / min (ratio: 100), and total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having bristles raised by buffing grinding with a grinding amount of 43 g / m ² and a maximum grinding load of 550 W / m was produced. The obtained polishing cloth had an average fiber diameter of 1.1 μm, a thickness of 0.52 mm, a basis weight of 169 g / m ² , and an apparent density of 0.325 g / cm ³ . The results are shown in Table 1.

[Example 3]
(raw cotton)
A sea island having a fineness of 5.4 dtex and a fiber length of 51 mm in the same manner as in Example 1 except that a discharge amount of 1.1 g / min · hole was made using a sea-island type composite base having 36 islands / hole. A raw cotton of type composite fiber was obtained.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using sandpaper with an average abrasive particle size of 55 μm (ratio of abrasive particle size / ultrafine fiber diameter: 21), paper speed of 1000 m / min, sheet speed of 8.0 m / min (ratio: 125), total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having napped bristles was produced by buffing grinding with a grinding amount of 75 g / m ² and a maximum grinding load of 900 W / m. The obtained abrasive cloth had an average fiber diameter of 2.6 μm, a thickness of 0.51 mm, a basis weight of 165 g / m ² , and an apparent density of 0.324 g / cm ³ . The results are shown in Table 1.

[Example 4]
(raw cotton)
A sea island having a fineness of 5.5 dtex and a fiber length of 51 mm in the same manner as in Example 2 except that PET having a melting point of 260 ° C. and MFR 46.5 was used as an island component, and a melting point of 85 ° C. and polystyrene having MFR 117 was used as a sea component. A raw cotton of type composite fiber was obtained.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using sandpaper with an average abrasive particle size of 55 μm (ratio of abrasive particle size / ultrafine fiber diameter: 55), a paper speed of 800 m / min, a sheet speed of 5.5 m / min (ratio: 145), total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having bristles raised by buffing grinding with a grinding amount of 54 g / m ² and a maximum grinding load of 630 W / m was produced. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 1.0 μm, a thickness of 0.53 mm, a basis weight of 168 g / m ² , and an apparent density of 0.317 g / cm ³ . The results are shown in Table 1.

[Example 5]
(raw cotton)
Same as Example 1 except that PET having a melting point of 260 ° C. and MFR 46.5 was used as an island component, and a copolymer PET obtained by copolymerizing 8 mol% of 5-sodium isophthalic acid having a melting point of 230 ° C. and MFR 100 was used as a sea component. As a result, raw cotton of sea-island type composite fiber having a fineness of 4.7 dtex and a fiber length of 51 mm was obtained.

(Extra-fine fiber generation type nonwoven fabric)
A non-woven fabric made of sea-island composite fibers having a basis weight of 695 g / m ² and an apparent density of 0.228 g / cm ³ was obtained in the same manner as in Example 1 except that the above-mentioned sea-island composite fiber raw cotton was used.

(Water-dispersed polyurethane liquid)
Add 4% by mass of sodium sulfate as a heat-sensitive gelling agent to nonionic forced emulsification type polyurethane emulsion (polycarbonate) relative to the solid content of polyurethane, and adjust the water-dispersed polyurethane liquid so that the polyurethane liquid concentration becomes 10% by mass. did.
(Polishing cloth)
The above-mentioned water-dispersed polyurethane liquid is applied to the nonwoven fabric composed of the sea-island type composite fibers, and is dried with hot air at a drying temperature of 120 ° C. for 5 minutes. The amount of polyurethane attached is 30% by mass with respect to the island components of the nonwoven fabric. A certain sheet with polyurethane was obtained.

The sheet with polyurethane was immersed in a 20 g / L sodium hydroxide aqueous solution heated to a temperature of 90 ° C. using a liquid dyeing machine, treated for 30 minutes, and sea components were dissolved and removed from the sea-island composite fibers. Thereafter, the paper is cut in the thickness direction by a half-cutting machine having an endless band knife, and the non-half-cut surface is sand paper having an average abrasive grain size of 55 μm (abrasive grain size / extra fine fiber diameter ratio: 82), and a paper speed of 1000 m / And a sheet speed of 10.0 m / min (ratio: 100), a three-stage buffing total buffing grinding amount of 43 g / m ² and a maximum grinding load of 530 W / m were buffed to produce a polishing cloth having raised napping. A polishing cloth was obtained in the same manner as in Example 1 except that. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 0.67 μm, a thickness of 0.52 mm, a basis weight of 173 g / m ² , and an apparent density of 0.333 g / cm ³ . The results are shown in Table 1.
[Example 6]
(raw cotton)
A single fiber fineness of 2.2 dtex and a fiber length of 51 mm were obtained in the same manner as in Example 1 except that a sea-island type composite base having 600 islands / hole was used and the discharge rate was 1.0 g / min / hole. A raw cotton of sea-island type composite fiber was obtained.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using sandpaper with an average abrasive particle size of 15 μm (ratio of abrasive particle size / ultrafine fiber diameter: 38), a paper speed of 800 m / min, a sheet speed of 5.5 m / min (ratio: 145), a total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having bristles raised by buffing grinding with a grinding amount of 19 g / m ² and a maximum grinding load of 210 W / m was produced. The obtained polishing cloth had an average fiber diameter of 0.40 μm, a thickness of 0.55 mm, a basis weight of 190 g / m ² , and an apparent density of 0.345 g / cm ³ . The results are shown in Table 1.

[Comparative Example 1]
(raw cotton)
The same raw material of sea-island type composite fiber having a single fiber fineness of 4.7 dtex and a fiber length of 51 mm, similar to that used in Example 1, was used.

(Extra-fine fiber generation type nonwoven fabric)
In the same manner as in Example 1, a nonwoven fabric made of ultrafine fiber generating fibers was obtained.

(Polishing cloth)
Using sandpaper with an average abrasive particle size of 55 μm (ratio of abrasive particle size / ultrafine fiber diameter: 75), a paper speed of 800 m / min, a sheet speed of 10.0 m / min (ratio: 80), and total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having raised napping was produced by buffing grinding with a grinding amount of 50 g / m ² and a maximum grinding load of 640 W / m. The obtained abrasive cloth had an average fiber diameter of 0.73 μm, a thickness of 0.53 mm, a basis weight of 172 g / m ² , and an apparent density of 0.325 g / cm ³ . Since the ratio of the paper speed to the sheet speed was as low as 80, grinding was not effective, the fiber length was sparse, the surface fibers were scattered, and the polishing performance was also the substrate surface roughness. The number of scratches was not satisfactory. The results are shown in Table 1.

[Comparative Example 2]
(raw cotton)
The same raw cotton as that of the sea-island type composite fiber used in Example 3 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Total buffing grinding of three-stage buffing with sandpaper having an average abrasive grain size of 15 μm (ratio of abrasive grain size / ultrafine fiber diameter: 6), paper speed of 1000 m / min, sheet speed of 10.0 m / min (ratio: 100) A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having napped bristles was produced by buffing grinding at an amount of 50 g / m ² and a maximum grinding load of 570 W / m. The obtained polishing cloth had an average fiber diameter of 2.6 μm, a thickness of 0.52 mm, a basis weight of 168 g / m ² , and an apparent density of 0.323 g / cm ³ . Since the ratio of the abrasive particle diameter to the fiber diameter was 6, grinding was not efficient because the abrasive particle diameter was too small, the fiber length was not sparse, and some surface fibers were not fused. It was. Also, regarding the polishing performance, neither the substrate surface roughness nor the number of scratches was satisfactory. The results are shown in Table 1.

[Comparative Example 3]
(raw cotton)
The same raw material of sea-island type composite fiber having a fineness of 5.5 dtex and a fiber length of 51 mm was used as in Example 4.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
A polishing cloth was obtained in the same manner as in Example 4, except that a buffing grinding was performed with buffing grinding at a maximum grinding load of 130 W / m and a raised buffing was produced, with a total buffing grinding amount of 3 steps buffing of 7 g / m ² . It was. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 1.0 μm, a thickness of 0.54 mm, a basis weight of 176 g / m ² , and an apparent density of 0.326 g / cm ³ . Since the grinding amount was 7 g / m ² and the grinding load was 130 W / m, grinding could not be performed sufficiently, the fiber length was not sparse, and polyurethane uncut residue was observed on the surface. . Also, regarding the polishing performance, neither the substrate surface roughness nor the number of scratches was satisfactory. The results are shown in Table 1.

[Comparative Example 4]
(raw cotton)
PET and polystyrene similar to those used in Example 4 were used as the sea component and the island component, respectively. Moreover, it is the same as that of Example 1 except that the island / sea mass ratio is 60/40, the discharge rate is 1.9 g / min / hole, and the island is made using a sea-island type composite base having 16 islands / hole. A raw cotton of a sea-island type composite fiber having a fineness of 3.6 dtex and a fiber length of 51 mm was obtained.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using a sandpaper with an average abrasive grain size of 75 μm (ratio of abrasive grain size / ultrafine fiber diameter: 21), a paper speed of 1000 m / min, a sheet speed of 10.0 m / min (ratio: 100), and total buffing of three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having a raised surface was produced by buffing grinding with a grinding amount of 43 g / m ² and a maximum grinding load of 460 W / m. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 3.5 μm, a thickness of 0.52 mm, a basis weight of 178 g / m ² , and an apparent density of 0.342 g / cm ³ . Since the fiber diameter of the polishing cloth was as thick as 3.5 μm, the tip of the ultrafine fiber on the surface was torn off, and no spherical protrusion was formed on the tip of the ultrafine fiber. Further, due to the large fiber diameter, the substrate surface roughness and the number of scratches were not satisfactory in terms of polishing performance. The results are shown in Table 1.

[Comparative Example 5]
(raw cotton)
The same raw cotton as that of the sea-island type composite fiber used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
Using a sandpaper with an average abrasive particle size of 75 μm (ratio of abrasive particle size / ultrafine fiber diameter: 103), a paper speed of 800 m / min, a sheet speed of 5.3 m / min (ratio: 151), and total buffing grinding with three-stage buffing A polishing cloth was obtained in the same manner as in Example 1 except that a polishing cloth having bristles raised by buffing grinding at an amount of 50 g / m ² and a maximum grinding load of 580 W / m was produced. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 0.73 μm, a thickness of 0.53 mm, a basis weight of 170 g / m ² , and an apparent density of 0.321 g / cm ³ . Since the ratio of the abrasive particle diameter to the fiber diameter was 103, the abrasive particle diameter was too large, so that grinding could not be performed efficiently, and the fiber length was sparse. Also, regarding the polishing performance, neither the substrate surface roughness nor the number of scratches was satisfactory. The results are shown in Table 1.

[Comparative Example 6]
(raw cotton)
The same raw cotton as that of the sea-island type composite fiber used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
First and second stage paper speeds of 800 m / min, sheet speed of 5.0 m / min (ratio: 160), third stage paper speed of 600 m / min, sheet speed of 5.0 m / min (ratio: 120), buffing the grinding amount of each stage and 20,15,5g / ^{m 2} (50:38:12), polishing with a buffing abrasive brushed been napped total buffing grinding amount 40 g / ^{m 2,} the maximum grinding load 1060W / m An abrasive cloth was obtained in the same manner as in Example 1 except that the cloth was produced. The obtained polishing cloth had an average fiber diameter of ultrafine fibers of 0.73 μm, a thickness of 0.52 mm, a basis weight of 171 g / m ² , and an apparent density of 0.329 g / cm ³ . Since the grinding ratio of the second stage was higher than that of the first stage, the effect of grinding much in the second stage remained even after finishing, and the surface state was not uniform. Moreover, since the grinding load was as high as 1060 W / m, fusion between the fibers was observed. As for the polishing performance, neither the substrate surface roughness nor the number of scratches was satisfactory. The results are shown in Table 1.

[Comparative Example 7]
(raw cotton)
The same raw cotton as that of the sea-island type composite fiber used in Example 1 was used.

(Extra-fine fiber generation type nonwoven fabric)
An ultrafine fiber-generating fiber nonwoven fabric was obtained in the same manner as in Example 1 except that the above-mentioned sea-island type composite fiber was used.

(Polishing cloth)
A three-stage buffing Total Buffing grinding amount 89 g / m ^2, except that to prepare a polishing cloth having a maximum grinding load is buffing grinding brushed with 870W / m nap, to obtain a polishing cloth in the same manner as in Example 1 It was. The obtained polishing cloth had an average fiber diameter of 0.73 μm, a thickness of 0.50 mm, a basis weight of 158 g / m ² , and an apparent density of 0.316 g / cm ³ . Since the grinding amount was as large as 89 g / m ² , many fiber fusions were observed due to grinding heat. Also, regarding the polishing performance, neither the substrate surface roughness nor the number of scratches was satisfactory. The results are shown in Table 1.

1: Spherical tip 2: Polygonal tip

Claims (4)

  A polishing cloth composed of a fiber entanglement mainly composed of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm and an elastic polymer, and having raised ultrafine fibers on the surface, and 50 of the raised ultrafine fibers. A polishing cloth characterized in that the tip of 0.0 to 100.0% of ultrafine fibers has a diameter of 120 to 300% of the fiber diameter. A sheet composed of a fiber entangled body mainly composed of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm and an elastic polymer is run, and an average abrasive 10 to 90 times the average fiber diameter of the ultrafine fibers. The sandpaper having a particle size is rotated in the direction opposite to the traveling direction of the sheet traveling at a speed of 100 to 160 times the sheet speed, the total grinding amount is 10 to 80 g / m ² , and the grinding load is 200 to 1000 W. A method for producing an abrasive cloth, characterized in that buffing is performed within a range of / m.   The method for producing an abrasive cloth according to claim 2, wherein the contact length between the sheet and the sandpaper is in the range of 5 to 50 mm during buffing grinding.   4. The method for producing an abrasive cloth according to claim 2, wherein the grinding clearance is 0.1 to 0.9 times the target thickness during buffing grinding.